The objectives of these studies are to identify and investigate the degree of tumor localization, selective organ localization and metabolic rates of specific biologically significant compounds labeled with short-lived nuclides. These labeled compounds will be evaluated as agents for early detection of cancer, will be used to define chemical and biological events leading to carcinogenic reactions and will be studied in normal and abnormal metabolic circumstances. The radionuclides used in the study are all produced in the cyclotron, have short half-lives which greatly reduce patient exposure and require detection apparatus suitable for high energy radiation. These studies will be evaluated in animals and man with quantitative scanning and imaging systems. Specific proposed studies in order of priority: 1) Nitrogen-13 Compounds for Tumor and Organ Imaging in Human Cancer Patients; 2) Evaluation of 11C-Amino Acids as Pancreatic Imaging or Tumor Localization Agents; 3) Evaluation of 11C-Thymidine as a Potential Tumor Localizing Agent; 4) In Vivo Disposition of N-13 Labeled Nitrate, Nitrite and Nitrosocarbaryl; and 5) Localization of Soft Tissue Tumors with 73Se-Selenite.